Electromagnetic drive type plunger pump

ABSTRACT

With the structure comprising a cylinder  10,  a magnetic circuit to exert mountain-shaped thrust, and a feeding spring  50  to exert urging force to the plunger  20  in a feeding process, fuel is sucked by the movement of the plunger  20  and energy is accumulated at the feeding spring  50  at a powering state, the fuel is fed by the movement of the plunger  20  by the urging force of the feeding spring  50  at a non-powering state, the spring constant of the feeding spring  50  is set to generate the urging force larger than the thrust in an early range of the mountain-shaped thrust, and the second spring  60  is disposed to exert the urging force in a direction against the urging force of the feeding spring  50  to make the urging force smaller than the thrust, at least in the early range.  
     In this manner, with an electromagnetically driven type plunger pump of a non-powering feeding type, the effective stroke is enlarged and the feeding amount is increased.

TECHNICAL FIELD

[0001] The present invention relates to an electromagnetically driven type plunger pump, which sucks and feeds a liquid such as engine fuel and so on, and especially relates to the electromagnetically driven type plunger pump of a non-powering feed type, which sucks a liquid by the movement of a plunger and accumulates energy at a spring at a powering state, and feeds the liquid with the accumulated energy at a non-powering state.

BACKGROUND ART

[0002] A conventional electromagnetically driven type plunger pump of a non-powering feed type comprises, for example, a plunger which is disposed in a cylinder (a cylindrical body) being free to reciprocate, a pair of springs which exert specific urging force to the plunger from both ends having consistent contact, a solenoid coil which exerts thrust (electromagnetic force) to the plunger to suck a liquid, a magnetic circuit including a yoke etc., various check valves, and so on.

[0003] A pair of springs are disposed to have consistent contact with the plunger, and dampen a vibration of the plunger while retaining it at a specific resting position at a non-powered resting state with energy of the springs released, or perform together as feeding springs to accumulate the energy for feeding.

[0004] Further, as shown in FIG. 7, the thrust (electromagnetic force) generated by the magnetic circuit has a characteristic that it is maximum when the plunger 3, which is urged by the pair of springs 2, is located at the vicinity of the yoke 1 which forms the magnetic circuit. In other words, the obtained thrust shows a mountain-shaped characteristic as being small at an early range and a later range, and being large at a middle range.

[0005] By the way, as shown in FIG. 8, with the electromagnetically driven type plunger pump, a threshold F0, which is determined by a target discharging pressure (a feeding pressure) and the diameter (the area) of the plunger, is present. Here, the plunger 3 cannot be moved towards the feeding direction when the urging force of the spring 2 does not exceed the threshold F0.

[0006] On the other hand, as shown in FIG. 8 with a two-dot chain line, it is ideal to obtain an effective stroke Si as large as possible with the spring constant ki of the spring 2 set relatively small, so that the feeding liquid amount (the discharged amount) is increased with the moving stroke of the plunger 3 increased as large as possible. However, in this case, as shown in FIG. 8 with oblique lines, the urging force of the spring 2 exceeds the thrust at the early range. Consequently, even if power is supplied at a sucking process, the plunger 3 cannot be operated and the compression of the spring 2, namely the accumulation of the energy, is not performed.

[0007] Therefore, as shown in FIG. 8, when the liquid discharging pressure (the feeding pressure) is set relatively high (200 kPa˜300 kPa, for example), and also with restrictions of the size of a product etc., the spring constant k of the spring 2 is set relatively large, resulting in that the effective stroke S of the plunger 3 is small. Accordingly, the discharging amount (the feeding amount) cannot be increased, and an increase of the power consumption or upsizing of the solenoid coil is needed to obtain a necessary discharging amount.

[0008] The present invention is accomplished in the light of the abovementioned points, and the purpose is to provide an electromagnetically driven type plunger pump which has a high efficient discharging (feeding) performance with the effective stroke of the plunger being large, while being in a quest of simplifying the structure, downsizing, reducing power consumption, reducing noise, and so on.

DISCLOSURE OF THE INVENTION

[0009] The electromagnetically driven type plunger pump of the present invention comprises a cylindrical body which forms a passage for a liquid, a plunger which is disposed having intimate contact in the passage of the cylindrical body being free to reciprocate within a specific range, a magnetic circuit including a solenoid coil which exerts mountain-shaped thrust to the plunger in accordance with the movement at a sucking process of the liquid, and a feeding spring which exerts urging force to the plunger at a feeding process, wherein the liquid is sucked by the movement of the plunger and energy is accumulated at the feeding spring at a powering state, the liquid is fed by the movement of the plunger with the energy released at a non-powering state, the spring constant of the feeding spring is set to generate urging force which is larger than the thrust in an early range of the mountain-shaped thrust, and a second spring is disposed to exert urging force to the plunger in a direction against the urging force of the feeding spring so that the urging force of the feeding spring is smaller than the thrust, at least in the early range.

[0010] With this structure, in the early range with relatively small thrust of mountain-shaped thrust characteristic curve, the urging force (load) of the feeding spring, which is set larger than the thrust (the spring constant is relatively small), is reduced to be smaller than the thrust by the urging force (load) of the second spring which urges in the direction against the feeding spring. Therefore, the thrust can move the plunger in this early range, and the moving stroke of the plunger is enlarged, namely, the energy accumulated at the feeding spring is increased, due to the spring characteristics of the feeding spring and the second spring. Hence, a high efficient discharging (feeding) characteristic is obtained and the discharging amount (the feeding amount) of the fuel is increased.

[0011] With the abovementioned structure, the second spring can be disposed to have contact and to exert the urging force to the plunger at least in the early range, and to be apart from the plunger at least in the ranges except for the early range.

[0012] With this structure, the second spring has contact and exerts the urging force to the plunger in the direction against the feeding spring at least in the early range, and only the urging force of the feeding spring is exerted to the plunger in the rest of the ranges. Therefore, compared with the case in which the second spring has consistent contact, the energy accumulated at the feeding spring can be increased.

[0013] With the abovementioned structure, it is possible to set the second spring to be apart from the plunger when the second spring extends to the free length.

[0014] With this structure, it is possible to make the structure simple, because the second spring leaves the plunger automatically when the second spring extends to the free length at which no urging force is generated.

[0015] With the abovementioned structure, the spring constant of the second spring can be set larger than the spring constant of the feeding spring.

[0016] With this structure, desired urging force can be obtained with the compressed length shortened. Hence, the pump can be downsized.

[0017] With the abovementioned structure, the second spring can be disposed at the opposite side of the feeding spring sandwiching the plunger.

[0018] With this structure, it is possible to reduce noise with a simple structure, because the plunger is supported from both sides by the springs.

[0019] With the abovementioned structure, the second spring can be disposed to surround the feeding spring at the outer side in the diameter direction.

[0020] With this structure, the compressed volume of when the plunger is at the full-stroke position can be reduced by the space for disposing of the second spring, and the compression rate of the fuel to be fed is increased. In this manner, the self-absorption capability can be improved.

[0021] With the abovementioned structure, it is possible for the plunger to have a liquid passage which pierces in the axis direction, and a valve body which is capable to open the liquid passage at the sucking process and to close the fuel passage at the feeding process, and the valve body is a poppet valve to perform the opening operation by moving outwards.

[0022] With this structure, because the outside area of the poppet valve is the space to be compressed, the compressed volume of when the plunger is at the full-stroke position can be reduced, and the compression rate of the fuel to be fed is increased, as mentioned above. In this manner, the self-absorption capability can be improved.

[0023] With the abovementioned structure, the second spring can be a coil spring with the section being rectangle-shape (angular shape).

[0024] With this structure, because the setting length of the second spring can be shortened, the compressed volume of when the plunger is at the full-stroke position can be reduced, and the compression rate of the fuel to be fed is increased. In this manner, the self-absorption capability can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025]FIG. 1 is a sectional view showing an embodiment of an electromagnetically driven type plunger pump of the present invention.

[0026]FIG. 2 is a characteristic diagram showing an operating characteristic of the electromagnetically driven type plunger pump shown in FIG. 1.

[0027]FIG. 3 is an enlarged partial sectional view to explain the operation of the electromagnetically driven type plunger pump shown in FIG. 1; and (a) shows a resting state, (b) shows a state of when the second spring extends to the free length, and (c) shows the state of when the plunger is apart from the second spring with a further movement.

[0028]FIG. 4 is a partial sectional view showing another embodiment of the electromagnetically driven type plunger pump.

[0029]FIG. 5 is a sectional view further showing another embodiment of the electromagnetically driven type plunger pump.

[0030]FIG. 6 is a partial sectional view further showing another embodiment of the electromagnetically driven type plunger pump.

BEST MODE FOR CARRYING OUT THE INVENTION

[0031] The embodiments of the present invention are explained in the following based on the attached drawings.

[0032]FIG. 1 is a sectional view showing an embodiment of an electromagnetically driven type plunger pump of the present invention. The electromagnetically driven type plunger pump of this embodiment feeds fuel for an engine etc. as a liquid. As shown in FIG. 1, it comprises a cylinder 10 as a cylindrical body which shape is cylindrical, a plunger 20 disposed in a passage of the cylinder 10 having intimate contact and being free to reciprocate, a magnetic circuit including a solenoid coil 30 and a yoke 40 etc. which generate electromagnetic force to exert thrust to the plunger 20, a feeding spring 50 which accumulates energy for feeding a liquid, a second spring 60 which generates urging force in the direction against the urging force of the feeding spring 50, and so on, as a basic structure.

[0033] The plunger 20 is a moving member having a specific length, which slides in the axis direction in the cylinder 10 with being free to reciprocate within a specific range. A fuel passage 20 a is formed in the plunger 20 as a liquid passage piercing in the reciprocating direction (the axis direction). Further, an enlarged passage 20 b is formed at one end (the downstream side of the fuel flow) as a liquid passage enlarging the fuel passage 20 a in the diameter direction.

[0034] A check valve 21 and a coil spring 22 which urges the check valve 21 towards the upstream side, namely towards the fuel passage 20 a, are disposed in the enlarged passage 20 b. A valve guide 23, which forms a part of the plunger 20 and has a guide passage 23 a in the center to guide a stem portion 21 a of the check valve 21, is fitted to the outer end portion of the enlarged passage 20 b. One end side of a coil spring 22 is held by an inner side end face 23 b of the valve guide 23. Here, a fuel passage 23 c is formed to the valve guide 23 at the outer side in the diameter direction of the guide passage 23 a.

[0035] Consequently, the fuel passage 20 a of the plunger 20 is closed consistently with the check valve 21 which is urged by the coil spring 22. Then, when a specific pressure difference or more occurs between the rooms (the fuel passage 20 a and the enlarged passage 20 b) which sandwich the check valve 21 (the pressure of the fuel passage 20 a side>the pressure of the enlarged passage 20 b side), the check valve 21 opens the fuel passage 20 a. Here, not limited to being hemisphere-shaped as shown in the figure, sphere-shaped or disc-shaped can also be possible as the check valve 21. Furthermore, the material can be resin such as rubber etc. or metal.

[0036] A pair of ring-shaped yokes 40, which consist of a cylindrical portion 40 a and a brim portion 40 b, are disposed respectively with a specific gap and facing each other, at the outer side of the cylinder 10. A bobbin 41 is attached to the cylindrical portions 40 a of the yokes 40, and a solenoid coil 30 for exciting is winded over the bobbin 41.

[0037] Then, by passing electric current through the solenoid coil in a specific direction, magnetic force lines are generated passing through a pair of the yokes 40, the plunger 20 etc., and the thrust (electromagnetic force) to move the plunger 20 towards the left in FIG. 1 is generated. As shown in FIG. 2, the characteristic of the thrust forms a mountain-shaped curve in accordance with moving strokes of the plunger 20.

[0038] An inlet side valve support member 70 and an outlet side valve support member 80 are fixed by fitting to both end portions of the cylinder 10 respectively. The feeding spring 50 is disposed between the inlet side valve support member 70 and one end portion of the plunger 20, and the second spring 60 is disposed between the outlet side valve support member 80 and the other end portion of the plunger 20.

[0039] The inlet side valve support member 70 is formed with a valve case 73 which accommodates a check valve 71 and a coil spring 72 and has a fuel passage 73 a, and a valve guide 74 which has a guide passage 74 a to guide a stem portion 71 a of the check valve 71. One end side of the coil spring 72 is held by an inner end face 74 b of the valve guide 74. Here, the valve case 73 is fitted to the cylinder 10 with an O-ring 75. At the valve guide 74 which is fitted to the valve case 73, a fuel passage 74 c is formed at the outer side in the diameter direction of the guide passage 74 a.

[0040] Consequently, the fuel passage 73 a of the valve case 73 is closed consistently with the check valve 71 which is urged by the coil spring 72. Then, when a specific pressure difference or more occurs between the rooms (the upstream side passage and the downstream side passage sandwiching the fuel passage 73 a) which sandwich the check valve 71 (the pressure of the upstream side>the pressure of the downstream side), the check valve 71 opens the fuel passage 73 a. Here, not limited to being hemisphere-shaped as shown in the figure, sphere-shaped or disc-shaped can be possible as the check valve 71. Furthermore, the material can also be resin such as rubber etc. or metal.

[0041] The outlet side valve support member 80 is formed with a valve case 83 which accommodates a check valve 81 and a coil spring 82 and has a fuel passage 83 a, and a valve guide 84 which has a guide passage 84 a to guide a stem portion 81 a of the check valve 81. One end side of the coil spring 82 is held by an inner end face 84 b of the valve guide 84. Here, the valve case 83 is fitted to the cylinder 10 with an O-ring 85. At the valve guide 84 which is fitted to the valve case 83, a fuel passage 84 c is formed at the outer side in the diameter direction of the guide passage 84 a.

[0042] Consequently, the fuel passage 83 a of the valve case 83 is closed consistently with the check valve 81 which is urged by the coil spring 82. Then, when a specific pressure difference or more occurs between the rooms (the upstream side passage and the downstream side passage sandwiching the fuel passage 83 a) which sandwich the check valve 81 (the pressure of the upstream side>the pressure of the downstream side), the check valve 81 opens the fuel passage 83 a. Here, not limited to being hemisphere-shaped as shown in the figure, sphere-shaped or disc-shaped can be possible as the check valve 71. Furthermore, the material can also be resin such as rubber etc. or metal.

[0043] Further, an inlet side connect pipe 91 is connected to the outer side of the inlet side valve support member 70 with an O-ring 90. The inlet side connect pipe 91 forms a fuel passage 91 a piercing in the axis direction. Furthermore, an outlet side connect pipe 93 is connected so as to cover the outlet side valve support member 80 and the cylinder 10 with an O-ring 92. The outlet side connect pipe 93 forms a fuel passage 93 a piercing in the axis direction.

[0044] The feeding spring 50 is a coil-shaped compression spring, and one end portion 50 a has consistent contact with one end face 20d of the plunger 20, and the other end portion 50 b has consistent contact with the inner side end face 73 b of the valve case 73. As shown in FIG. 2, the feeding spring 50 is set to have a relatively small spring constant k1, so that the generated urging force (load) F1 is larger than the thrust (load) in the early range and the later range which are the left side base part and the right side base part of the mountain-shaped thrust respectively.

[0045] The second spring 60 is a coil-shaped compression spring. It is disposed and fixed so that one end portion 60 a is free to be in contact with or apart from the other end face 20 e of the plunger 20, and the other end portion 60 b is in contact with and not apart from a tubular groove bottom portion 83 b of the valve case 83. As shown in FIG. 2, the second spring 60 is set to have a relatively large spring constant k2 (larger than the spring constant k1 of the feeding spring 50), so that the urging force (load) F2 is exerted to the plunger 20 in the direction against the urging force F1 of the feeding force 50 in the early range which is the left side base of the mountain-shaped thrust and in a part of the middle range.

[0046] Regarding the performance of the second spring 60, because the urging force F2 directs against the urging force F1 of the feeding spring 50, it acts so as to eliminate the urging force of the feeding spring 50 in the abovementioned specific range.

[0047] Therefore, the resultant force F of the urging force F1 and the urging force F2 is zero (point P0) at the point of the intersection of the urging force F1 line and the urging force F2 line. At the point where the urging force F2 of the second spring 60 is zero, only the urging force F1 of the feeding spring 50 remains (point P1). After this point, the resultant force traces the line of the urging force F1 of the feeding spring 50 passing through the intersection (point P2) with the thrust curve. Hence, it is a polygonal line as a whole.

[0048] In this manner, the urging force of the feeding spring 50 is smaller than the thrust as a result, in the early range where the urging force F1 of the feeding spring 50 is set larger than the thrust, so that the thrust can drive the plunger 20.

[0049] Further, the moving stroke Sn of the plunger 20 is the distance between point P3, which is the intersection of the polygonal line indicating the resultant force F and threshold line, and point P4, which is the intersection between a perpendicular line passing through point P2 and threshold line, and is larger than the conventional stroke S. Furthermore, compared with the conventional structure, the effective energy which is accumulated at the feeding spring 50 is increased by the amount which corresponds to the area surrounded with points P1, P2, P5 and P3. Hence, a high efficient discharging (feeding) characteristic is obtained and the discharging amount (the feeding amount) of the fuel is increased than that of the conventional structure.

[0050] Next, the operation of the electromagnetically driven type plunger pump of the abovementioned embodiment is explained in accordance with FIG. 1 through FIG. 3. Firstly, the plunger 20 stays at the position (point P0) where the urging force of the feeding spring 50 and that of the second spring 60 balance at the non-powering state in which the solenoid coil 30 is not powered.

[0051] At this resting state, when the solenoid coil 30 is powered and the electromagnetic force (the thrust) is generated, the plunger 20 is pulled towards the upstream side (towards the left side in FIG. 1) to start the going movement. The upstream side room Su is reduced, and the downstream side room Sd is expanded. At this time, as shown in FIG. 1 and FIG. 3 (a), the pressure in the downstream side room Sd decreases because the check valve 81 closes the fuel passage 83 a. Then, when the pressure in the upstream side room Su becomes larger than the pressure in the downstream side room Sd by a specific value, the check valve 21 opens the fuel passage 20 a against the urging force of the coil spring 22. In this manner, the fuel in the upstream side room Su is sucked into the downstream side room Sd passing through the fuel passage 20 a.

[0052] Then, as shown in FIG. 2 and FIG. 3 (b), when the plunger 20 moves a specific distance to reach point P1′, the second spring 60 extends to the free length and exerts no urging force to the plunger 20. At the same time, only the urging force F1 of the feeding spring 50 starts to act as spring urging force to the plunger 20.

[0053] As shown in FIG. 3 (c), when the plunger 20 moves further, the free end portion 60 a of the second spring 60 is completely apart from the end face 20 e of the plunger 20. Then, when the plunger reaches point P2′ in FIG. 2, the thrust by the electromagnetic force and the urging force F1 of the feeding force 50 balance (point P2), and the check valve 21 closes the fuel passage 20 a at the same time when the plunger 20 stops. The abovementioned movement (the going movement) of the plunger 20 corresponds to a sucking process of the fuel. In this sucking process, the feeding spring 50 is compressed so that the energy of the elastic deformation is accumulated.

[0054] Next, when the powering to the solenoid coil 30 is cut off, the thrust by the electromagnetic force is eliminated, and only the urging force F1 of the feeding spring 50, which is increased by the compression, is exerted. As a result, the plunger 20 starts the returning movement towards the downstream side (towards the right side in FIG. 1). By this returning movement, the fuel sucked into the downstream side room Sd begins to be compressed. When it reaches a specific pressure, the check valve 81 opens the fuel passage 83 a against the urging force of the coil spring 82. In this manner, the fuel filled in the downstream side room Sd is discharged (fed) through the outlet side connect pipe 93 at the specific pressure.

[0055] Meanwhile, as the upstream side room Su is expanded, when the pressure of the upstream side room Su is decreased to be smaller than the pressure of the fuel passage 91 a in the inlet side connect pipe 91 by a specific value or more, the check valve 71 opens the fuel passage 73 a against the urging force of the coil spring 72. In this manner, the fuel at the upstream of the inlet side connect pipe 91 flows into the upstream side room Su through the fuel passage 73 a to be ready for the next sucking process.

[0056] Here, the check valve 71 allows the fuel at the specific pressure or more to flow into the upstream side room Su, and prevents to flow back, so as to contribute to reducing the self-absorption time.

[0057] The abovementioned movement (the returning movement) of the plunger 20 corresponds to a feeding process (a discharging process) of the fuel, and the movement is performed only by the accumulated energy at the feeding spring 50. As shown in FIG. 2, in this feeding process, the effective stroke Sn of the plunger 20 is larger than the conventional effective stroke S, and the effective energy accumulated at the feeding spring 50 is also larger. Hence, a high efficient discharging (feeding) characteristic is obtained and the discharging amount (the feeding amount) of the fuel is increased than that of the conventional structure.

[0058]FIG. 4 shows another embodiment of the electromagnetically driven type plunger pump, which check valve 21 to open and close the fuel passage 20 a of the plunger 20 is modified from the abovementioned embodiment. Here, the same numerical note is given to the same structure as the abovementioned embodiment to omit the explanation.

[0059] With the electromagnetically driven type plunger pump of this embodiment, a valve seat member 100 is fitted to the enlarged passage 20 b of the plunger 20. As a valve body, a poppet valve 110 is disposed being free to reciprocate so as to seat on a seat surface 101 a which is located at an end portion of a fuel passage 101 formed in the valve seat member 100. Further, a coil spring 111 is disposed to urge the poppet valve 110 to close the fuel passage 101 consistently.

[0060] With this structure, because the enlarged passage 20 b and the downstream side room Sd are disconnected in the fuel feeding process, the compression rate of the fuel is increased by the volume of the enlarged passage 20 b. Hence, the self-absorption capability (the self-priming) can be further improved.

[0061]FIG. 5 further shows another embodiment of the electromagnetically driven type plunger pump of the present invention. Compared with the abovementioned embodiments shown in FIG. 1 and FIG. 4, the shape of the plunger 20 and the disposed position of the second spring 60 etc. are changed. Here, the same numerical note is given to the same structure as the abovementioned embodiment to omit the explanation.

[0062] With the electromagnetically driven type plunger pump of this embodiment, a plunger 120 which slides in the cylinder 10 comprises a fuel passage 120 a which extends in the axis direction, an enlarged passage 120 b which is located at the downstream side of the fuel passage 120 a, a spring hold portion 121 which is located at the upstream side of the fuel passage 120 a, a flange portion 122 which is located at the end portion of the upstream side, and so on.

[0063] Then, the poppet valve 110 and the coil spring 111, as shown in FIG. 4, are disposed in the enlarged passage 120 b. The outlet side valve support member 80 which supports the check valve 81 and the coil spring 82 is disposed at the downstream side. The outlet side connect pipe 93 is connected at the further downstream side.

[0064] A ring-shaped spring support member 130 is fitted to the upstream side end portion of the cylinder 10, and an inlet side connect pipe 91′ is connected so as to fit to the outer circumference of the spring support member 130. Then, a feeding spring 150 is disposed in the spring hold portion 121 of the plunger 120. The feeding spring 150 is held with one end having contact with a bottom face 121 a and the other end having contact with an inner end face 91 b of the inlet side connect pipe 91′.

[0065] Further, a second spring 160 is disposed between the spring support member 130 and the flange portion 122, at the outer circumference area of the plunger 120. The second spring 160 is disposed so that one end is fixed to an end face 130 a of the spring support member 130, and the other end is free to be in contact with or apart from the flange portion 122.

[0066] The feeding spring 150 and the second spring 160 are set to have the characteristics as shown in FIG. 2, and the operations are the same as those of the abovementioned embodiment.

[0067] With this structure, because the second spring 160 is disposed so as to surround the feeding spring 150 at the outer side in the diameter direction, the volume of the downstream side room Sd is decreased to a minimum when the plunger 120 is at the full-stroke position. In this manner, along with the advantage of the poppet valve 110, the compression rate of the fuel is increased and the self-absorption capability can be further improved.

[0068] In addition, with this embodiment, as a check valve is not disposed at the inlet side of the upstream side room Su, the fuel passage 91 a′ and the upstream side room Su are consistently connected, and the rest of the operations is the same as that of the abovementioned embodiment.

[0069]FIG. 6 further shows another embodiment of the electromagnetically driven type plunger pump of the present invention. Compared with the abovementioned embodiment shown in FIG. 4, the second spring 60 is modified. Here, the same numerical note is given to the same structure as the abovementioned embodiment to omit the explanation.

[0070] With the electromagnetically driven type plunger pump of this embodiment, a second spring 260 with the section being rectangle-shape (angular shape) is disposed in the downstream side room Sd which is located at the downstream side of the plunger 20. The second spring 260 is a coil spring being set to have the same characteristic as that of the abovementioned second spring 60. It is disposed so that one end is free to be in contact with or apart from an end face 100 a of the valve seat member 100 which supports the poppet valve 110 and the coil spring 111, and the other end is fixed to an end face 83 b′ of the valve case 83 which constitutes the outlet side valve support member 80.

[0071] With the electromagnetically driven type plunger pump of this embodiment, a second spring 260 with the section being rectangle-shape (angular shape) is disposed in the downstream side room Sd which is located at the downstream side of the plunger 20. The second spring 260 is a coil spring being set to have the same characteristic as that of the abovementioned second spring 60. It is disposed so that one end is free to be in contact with or apart from an end face 100 a of the valve seat member 100 which supports the poppet valve 110 and the coil spring 111, and the other end is fixed to an end face 83 b′ of the valve case 83 which constitutes the outlet side valve support member 80.

[0072] With this structure, because the second spring 260 is a coil spring with the section being rectangle-shape, the compressed length can be shortened so that the volume of the downstream side room Sd is further reduced (decreased) when the plunger 20 is at the full-stroke position. In this manner, along with the advantage of the poppet valve 110, the compression rate of the fuel is increased and the self-absorption capability (self-priming) can be further improved.

[0073] With the abovementioned embodiments, the plunger, such as 20, 120, 220, in which the fuel passage is formed piercing in the axis direction, is adopted as an application of the present invention. However, not limited to this, it is certainly possible to apply the present invention, for example, to a type wherein the plunger is solid, the going movement of the plunger sucks fuel into the downstream side room Sd through the fuel passage formed at a side face of the cylinder 10, and the returning movement of the plunger feeds fuel thereafter.

[0074] Furthermore, with abovementioned embodiments, fuel for an engine etc. (gasoline, light oil) is handled as a liquid to be sucked and fed. However, not limited to this, it is possible to handle various liquids such as water, oil and so on, as long as it is a liquid.

Industrial Applicability

[0075] As mentioned above, with an electromagnetically driven type plunger pump of the present invention, the spring constant of a feeding spring, which generates drive force for non-powering feeding (discharging), is set to generate urging force which is larger than thrust in an early range of mountain-shaped thrust (electromagnetic force) in accordance with moving strokes of a plunger, and a second spring is disposed to exert urging force to the plunger in a direction against the urging force of the feeding spring so that the urging force of the feeding spring is smaller than the thrust, at least in the early range. Because of this structure, the plunger can be moved by the thrust in this early range, and the moving stroke of the plunger and the accumulated energy at the feeding spring are increased due to the spring characteristics of the feeding spring and the second spring. In this manner, a high efficient discharging (feeding) characteristic is obtained and the discharging amount (the feeding amount) of the fuel is increased.

[0076] Further, the structure can be simplified by setting the position where the exerting of the urging force of the second spring stops to be the position where the second spring extends to the free length.

[0077] Furthermore, by disposing the second spring at the outer side in the diameter direction of the feeding spring, adopting a poppet valve as a valve body which is located at the downstream side of the plunger, or adopting a coil spring with the section being rectangle-shape as the second spring, the compressed volume of when the plunger is at the full-stroke position can be reduced, and the compression rate of the fuel to be fed is increased. In this manner, the self-absorption capability can be improved. 

1. An electromagnetically driven type plunger pump, comprising: a cylindrical body which forms a passage for a liquid; a plunger which is disposed having intimate contact in said passage of said cylindrical body being free to reciprocate within a specific range; a magnetic circuit including a solenoid coil which exerts mountain-shaped thrust to said plunger in accordance with the movement at a sucking process of the liquid; and a feeding spring which exerts urging force to said plunger at a feeding process; wherein the liquid is sucked by the movement of said plunger and energy is accumulated at said feeding spring at a powering state; the liquid is fed by the movement of said plunger with said energy released at a non-powering state; the spring constant of said feeding spring is set to generate urging force which is larger than said thrust in an early range of said mountain-shaped thrust; and a second spring is disposed to exert urging force to said plunger in a direction against the urging force of said feeding spring so that the urging force of said feeding spring is smaller than said thrust, at least in said early range.
 2. The electromagnetically driven type plunger pump according to claim 1, wherein said second spring is disposed to have contact and to exert the urging force to said plunger at least in said early range, and to be apart from said plunger at least in the ranges except for said early range.
 3. The electromagnetically driven type plunger pump according to claim 2, wherein said second spring is to be apart from said plunger when said second spring extends to the free length.
 4. The electromagnetically driven type plunger pump according to any one of clams 1 through 3, wherein the spring constant of said second spring is set larger than the spring constant of said feeding spring.
 5. The electromagnetically driven type plunger pump according to any one of claims 1 through 4, wherein said second spring is disposed at the opposite side of said feeding spring sandwiching said plunger.
 6. The electromagnetically driven type plunger pump according to any one of claims 1 through 4, wherein said second spring is disposed to surround said feeding spring at the outer side in the diameter direction.
 7. The electromagnetically driven type plunger pump according to any one of claims 1 through 6; wherein said plunger has a liquid passage which pierces in the axis direction, and a valve body which is capable to open said liquid passage at said sucking process and to close said fuel passage at said feeding process; and said valve body is a poppet valve to perform the opening operation by moving outwards.
 8. The electromagnetically driven type plunger pump according to any one of claims 1 through 7, wherein said second spring is a coil spring with the section being rectangle-shape. 